This pattern of substance use becomes more common as teenagers grow into young adults, and is likely to contribute to increased risk of poor physical and mental health outcomes.

Dr Hermens points out that people with mental health issues are significantly more likely to develop serious health problems and to die early.

"Traditionally there have been mental health services, and substance abuse services, but both have been quite separate. Our study shows that we need to integrate mental health interventions with substance use interventions in order to help at-risk young people," said Dr Hermens.

"There is a lot of evidence for the co-morbidity of mental health problems and substance misuse. More people have both mental health and substance use problems than either alone - in other words, it's the rule rather than the exception."

In a study published in BMJ Open, Dr Hermens and a team of researchers collected information from more than 2000 young people aged 12 to 30, who attended University-led headspace youth mental health clinics in Camperdown and Campbelltown.

Young people seeking help for a wide range of mental health problems provided information on their weekly consumption of alcohol, tobacco and cannabis, with 500 giving more detailed information on their pattern of alcohol consumption.

One in eight (12 percent) of young teens aged 12 to 17 drank alcohol at least once a week, rising to almost four out of 10 (39 percent) of 18-19 year olds, and increasing further to close to half of those aged 20 to 30.

Those in the youngest age group were twice as likely to say they drank alcohol every week as their peers in the general population.

And a significant proportion of those who provided more detailed information on their alcohol consumption were "risky" drinkers, with almost half of those with bipolar disorder falling into this category.

Some 7 percent of young teens said they used cannabis at least once a week. The equivalent figures for the other two age groups were 14 percent and 18 percent, respectively.

And those in the two younger age groups were more likely to smoke cannabis every day than they were to drink alcohol (3.6 percent versus 1.5 percent and 8.8 percent versus 6.0 percent respectively).

Almost one in four (23 percent) of young teens admitted to smoking cigarettes daily, as did one in three (36 percent) of older teens and four out of 10 (41 percent) of those aged 20 to 30.

The average age at which these patterns started was 15. And those who used any or all of the three substances were more likely to be male, older, and to have psychotic or bipolar disorders.